I have most of the batting leaderboards done; after they're finished I'll start on the pitching leaders. It's a slow process, made more so by the occasional lack of cooperation by the Play Index Finder (maybe it's a problem with my pc or internet, who knows).
Some observations thus far:
Bryce Harper's epic 2015 season set Millennial records in OBP, SLG, OPS, OPS+, and runs created. It's already looking like a fluke season... or, more likely (as Bill James opined), like Reggie Jackson's 1969 season: a performance he will never top even if he goes on to a long Hall-of-Fame career.
Mike Trout crossed the 3,000-PA threshold in 2016, meaning he now qualifies for career leaderboards (Harper is still 230 PA short). Among Millennials, Trout ranks 7th in BA, 2nd in OBP (to Joey Votto), 2nd in SLG (to Miguel Cabrera), and 1st in OPS. In OPS+ (which adjusts for league and ballpark effects), Trout is way ahead; Votto is a distant 2nd, followed by Miggy.
The Reds' Billy Hamilton ignominiously set the Millennial caught stealing record his rookie year, with 23. He's been a much more efficient base-stealer since then (he currently ranks 8th among his peers in career SB%), but he still has yet to crack the Millennial top 10 in stolen bases, simply because he hasn't played a full season since his rookie year of 2014. The only thing keeping him from 80 steals and the Millennial single-season record is durability.